1. Field of the Invention
The invention relates generally to systems and methods for landing and tying back riser strings in subsea wellhead fields containing multiple wellheads.
2. Description of the Related Art
Prior art methods are known for landing and tying back risers using funnels to land the riser onto a subsea wellhead housing. The funnels are helpful in docking the riser onto the wellhead housing and guiding the riser into the center of the docking opening on the housing. However, these methods are problematic since the funnel must normally be disposed though the moonpool of a floating vessel, and this can be quite difficult, particularly where the floating vessel is very long, such as in the case of a spar. This may result in damage to the funnel and make it difficult to ultimately land and dock the riser.
A subsea production system is described. The system includes a wellhead field having multiple wellheads and utilizes a stackable guide funnel system for sequential tying back of those wellheads. In a preferred embodiment, at least one of the wellheads is provided with a storage frame that retains several guide funnels that are nestably stacked one upon the other. The guide funnels may be sequentially removed from the frame by a riser connector having a complimentary latching mechanism. In a preferred embodiment, the frame is made up of a plurality of guide members that are secured to the exposed tubular conductor of the wellhead. A pair of annular rings surrounds portions of each of the guide members. The upper end of the frame is outwardly flared to assist in landing of the riser connector. The lower ring assists in landing the stackable guide funnel structure onto the wellhead.
A method is also described for sequential completion of wellheads within a wellhead field. In the method, a plurality of guide funnels are propositioned at one or more central locations upon the sea floor. The guide funnels are configured at the central location to permit sequential retreival. In a presently preferred embodiment, the guide funnels are nestably stacked one upon the other and retained within a storage frame for ease of retreival. A riser having a riser connector is lowered to the central location. The riser connector latches onto the uppermost guide funnel within the frame. The riser, together with the affixed funnel, is then lifted upwardly, removing the affixed funnel from the frame. The riser is then moved laterally through the sea until the funnel and riser are proximate a second wellhead within the wellhead field. The riser next is lowered to mate the riser connector with the tubular conductor of the second wellhead. The skirt of the guide funnel assists in this mating operation by guiding the tubular conductor toward the riser conductor. A second riser can then be lowered from the surface and latched into the next guide funnel available at the central location.